The effect of primary treatment and flow regime on clogging development in horizontal subsurface flow constructed wetlands: An experimental evaluation

The effect of both the type of primary treatment (hydrolitic up-flow sludge blanket (HUSB) reactor and conventional settling) and the flow regime (batch and continuous) on clogging development in subsurface flow constructed wetlands (SSF CWs) was studied. Clogging indicators (such as accumulated solids, hydraulic conductivity and drainable porosity) were determined in an experimental plant with three treatment lines. Correlations were encountered between the solids accumulated and both saturated hydraulic conductivity and drainable porosity reduction over time (74.5% and 89.2% of correlation, respectively). SSF CW implemented with a HUSB reactor accumulated ca. 30% lower sludge (1.9 kg DM/m2) than a system with a settler (2.5–2.8 kg DM/m2). However, no significant differences were recorded among treatment lines concerning hydraulic parameters (such as hydraulic conductivity or porosity). Root system development contributed to clogging. Accordingly, planted wetlands showed between 30% and 40% and 10% lower hydraulic conductivity and porosity reduction, respectively, than non-planted wetlands.

► Wetlands implemented with a HUSB reactor accumulated ca. 30% lower sludge than a system with a conventional settler as primary treatment.
► No significant differences on accumulated solids were found between SSF CW operated under batch or continuous regime.
► Macrophytes greatly contributed to clogging. Accordingly, after three years of operation roots accumulation in planted wetlands represented 35–70% of the total accumulated solids.
► Hydraulic conductivity and drainable porosity are well correlated to accumulated solids (74.5% and 89.2%, respectively). Therefore, they can be considered reliable techniques for indirect measurements of clogging.